In mechanical watches, time is broken down into fractions by a regulating member that today is usually a sprung balance. The latter is made up of three main parts: the balance, which acts as an inertia wheel; an arbor ending with pivot, which makes it possible to mount the balance in a timepiece frame; and a balance spring that produces a return torque proportional to the angular travel of the balance.
Reducing friction of the pivots allows a direct reduction of their wear, as well as an improved power reserve of the watch. Considerable work has been done on the subject, regarding the optimization of the bearings or lubrication of the pivot zones.
More recently, application EP 1,736,838, in the applicant's name, described an oscillator with no pivot, comprising an inertia wheel centered on the geometric oscillation axis of the oscillator, that wheel being connected to the frame of the movement by four springs, deforming during the oscillation and acting as the balance spring. The system, which is particularly interesting to reduce friction, since it does not comprise a pivot, is nevertheless limited. On the one hand, its oscillation amplitude is limited, less than or equal to 5°. On the other hand, the guiding offered by the flexible blades is not optimal, the geometric oscillation axis being able to suffer disruptions, by undergoing micro-movements, influencing the isochronism of the adjusting member.
The present invention aims to propose an oscillator providing the advantages of the systems of the state of the art, but at least partially free of their drawbacks. Brief description of the invention
To that end, the invention relates to a rotating oscillator with a virtual pivot, i.e., with no physical pivot in the usual sense of the term, which comprises a support element designed to allow the oscillator to be assembled on a timepiece, a balance, a plurality of flexible blades connecting the support element to the balance able to exert a return torque on the balance, and a felloe mounted secured to the balance.
According to the invention, the plurality of flexible blades comprises at least two flexible blades, a first blade of which is positioned in a first plane perpendicular to the plane of the oscillator, and a second blade that is positioned in a second plane perpendicular to the plane of the oscillator and intersecting the first plane, the first and second blades have an identical geometry, and in that the geometric oscillation axis of the oscillator is defined by the intersection of the first plane and the second plane, said geometric oscillation axis crossing the first and second blades at ⅞th of their respective lengths.
Other advantageous features of the invention are defined in the claims.
Consequently, the invention makes it possible to provide an inherent rotation, i.e., in which the oscillation axis is stationary, and without friction, other than that with the air. Quality factors of the oscillator are thus obtained that are typically greater by an order of magnitude relative to the oscillators of the state of the art, which reflects a reduction in the damping of the oscillation. This unique rotation makes it possible to produce a return torque on the oscillator that is practically proportional to the angular travel. A mechanical oscillator is obtained capable of offering a great potential to increase the power reserve of a mechanical watch.